The present invention relates to a support in the form of a protected disk, used for the recording and optical reading of information arranged in the form of coplanar tracks centered with respect to a rotation axis. The information is contained on a carrier layer formed from a material, whose optical properties are modified under the action of a light beam.
Disk structures for the optical recording of information are generally formed by a light radiation-sensitive layer deposited on a rigid support. To protect the sensitive layer from mechanical damage which can be caused by an external agent, it is known to confine it between two plates forming the walls of a protective enclosure. Another method consists of depositing a thick protective layer on the sensitive layer, which is itself supported by a substrate. However, this procedure has a number of important disadvantages. The thick protective layer deposited on the sensitive layer leads to a drop in the sensitivity of the layer to the inscription radiation. In addition, any sublimation or decomposition products which may have formed cannot be freed, which is prejudicial to the quality of the inscription. This has led to optical disks being produced with a protective enclosure. This protective method consists of providing above the sensitive layer, a closed space in the form of an annular chamber by means of spacers inserted between two plates or by a cap-like configuration given to either of the aforementioned members. The structures of the protected optical disk then comprise a first element supporting the sensitive layer and a second element integral with the first.
It is known to join these two elements by their central and peripheral areas, either by means of joined spacers, or by the cap-like configuration given to one of them, fixing also being ensured by the central and peripheral areas of the structure. Although this type of structure leads to the sensitive layer being well protected against mechanical agents and moisture, it leads to certain disadvantages. Thus, the structures of the protected optical disk may deform, e.g. camber or bend, under the action of differential expansions between the elements due to the action of external agents on the materials used for producing these elements, optionally due to the contraction of the weld bead used for fixing them, or for any other reason, such as heat moisture, etc. However, if these deformations are of a minimal magnitude, they are very prejudicial to the flatness and smoothness of the recording-carrying layer, because the information is generally in the form of microscopic elements resulting from the interaction of the layer with a finely focused radiation beam. A solution using two protective plates surrounding a layer support with central and peripheral connections can lead to untimely deformations.